scholarly journals Cardiac Alternans Occurs through the Synergy of Voltage- and Calcium-Dependent Mechanisms

Membranes ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 794
Author(s):  
Minh Tuan Hoang-Trong ◽  
Aman Ullah ◽  
William Jonathan Lederer ◽  
Mohsin Saleet Jafri
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Calcium Channels ◽  
Calcium Release ◽  
Ryanodine Receptors ◽  
Cellular Level ◽  
Open Probability ◽  
Calcium Dependent ◽  
Cardiac Alternans ◽  
Rapid Pacing ◽  
Dependent Mechanism

Cardiac alternans is characterized by alternating weak and strong beats of the heart. This signaling at the cellular level may appear as alternating long and short action potentials (APs) that occur in synchrony with alternating large and small calcium transients, respectively. Previous studies have suggested that alternans manifests itself through either a voltage dependent mechanism based upon action potential restitution or as a calcium dependent mechanism based on refractoriness of calcium release. We use a novel model of cardiac excitation-contraction (EC) coupling in the rat ventricular myocyte that includes 20,000 calcium release units (CRU) each with 49 ryanodine receptors (RyR2s) and 7 L-type calcium channels that are all stochastically gated. The model suggests that at the cellular level in the case of alternans produced by rapid pacing, the mechanism requires a synergy of voltage- and calcium-dependent mechanisms. The rapid pacing reduces AP duration and magnitude reducing the number of L-type calcium channels activating individual CRUs during each AP and thus increases the population of CRUs that can be recruited stochastically. Elevated myoplasmic and sarcoplasmic reticulum (SR) calcium, [Ca2+]myo and [Ca2+]SR respectively, increases ryanodine receptor open probability (Po) according to our model used in this simulation and this increased the probability of activating additional CRUs. A CRU that opens in one beat is less likely to open the subsequent beat due to refractoriness caused by incomplete refilling of the junctional sarcoplasmic reticulum (jSR). Furthermore, the model includes estimates of changes in Na+ fluxes and [Na+]i and thus provides insight into how changes in electrical activity, [Na+]i and sodium-calcium exchanger activity can modulate alternans. The model thus tracks critical elements that can account for rate-dependent changes in [Na+]i and [Ca2+]myo and how they contribute to the generation of Ca2+ signaling alternans in the heart.

scholarly journals The Effect of Calcium Ionophores on Fragmented Sarcoplasmic Reticulum

1972 ◽  
Vol 60 (6) ◽  
pp. 735-749 ◽  
Author(s):  
Antonio Scarpa ◽  
Judith Baldassare ◽  
Giuseppe Inesi
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Calcium Binding ◽  
Calcium Release ◽  
Atp Hydrolysis ◽  
Divalent Cations ◽  
Electron Microscopic ◽  
Microscopic Appearance ◽  
Calcium Accumulation ◽  
Calcium Dependent ◽  
Dependent Atpase

X-537 A and A 23187, two antibiotics which form liphophilic complexes with divalent cations, function as ionophores in vesicular fragments of sarcoplasmic reticulum (SR). Addition of either ionophore to SR preloaded with calcium in the presence of adenosine triphosphate (ATP), causes rapid release of calcium. Furthermore, net calcium accumulation by SR is prevented, when the ionophores are added to the reaction mixture before ATP. On the contrary, ATP-independent calcium binding to SR is not inhibited. This effect is specific for the two antibiotics and could not be reproduced, either by inactive derivatives, or by other known ionophores. Neither ionophore produces alterations of the electron microscopic appearance of SR membranes or inhibition of the calcium-dependent ATPase. In fact, the burst of ATP hydrolysis obtained on addition of calcium, is prolonged in the presence of the ionophores. Lanthanum inhibits ATP-independent calcium binding to SR, ATP-dependent calcium accumulation and calcium-dependent ATPase. However, addition of lanthanum to SR preloaded in the presence of ATP, does not cause calcium release. The reported experiments indicated that: (a) ATP-dependent calcium accumulation by SR results in primary formation of calcium ion gradients across the membrane. (b) Most of the accumulated calcium is not available for displacement by lanthanum on the outer surface of the membrane. (c) Calcium ionophores induce rapid equilibration of the gradients, by facilitating cation diffusion across the membrane.

NF-κB activation by depolarization of skeletal muscle cells depends on ryanodine and IP3 receptor-mediated calcium signals

2007 ◽  
Vol 292 (5) ◽  
pp. C1960-C1970 ◽  
Author(s):  
Juan Antonio Valdés ◽  
Jorge Hidalgo ◽  
José Luis Galaz ◽  
Natalia Puentes ◽  
Mónica Silva ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Calcium Release ◽  
Ryanodine Receptors ◽  
Field Potential ◽  
Muscle Cells ◽  
Skeletal Muscle Cells ◽  
Ip3 Receptor ◽  
Pharmacological Agents ◽  
Calcium Dependent ◽  
Element Binding Protein

Depolarization of skeletal muscle cells by either high external K+ or repetitive extracellular field potential pulses induces calcium release from internal stores. The two components of this release are mediated by either ryanodine receptors or inositol 1,4,5-trisphosphate (IP3) receptors and show differences in kinetics, amplitude, and subcellular localization. We have reported that the transcriptional regulators including ERKs, cAMP/Ca2+-response element binding protein, c- fos, c- jun, and egr-1 are activated by K+-induced depolarization and that their activation requires IP3-dependent calcium release. We presently describe the activation of the nuclear transcription factor NF-κB in response to depolarization by either high K+ (chronic) or electrical pulses (fluctuating). Calcium transients of relative short duration activate an NF-κB reporter gene to an intermediate level, whereas long-lasting calcium increases obtained by prolonged electrical stimulation protocols of various frequencies induce maximal activation of NF-κB. This activation is independent of extracellular calcium, whereas calcium release mediated by either ryanodine or IP3 receptors contribute in all conditions tested. NF-κB activation is mediated by IκBα degradation and p65 translocation to the nucleus. Partial blockade by N-acetyl-l-cysteine, a general antioxidant, suggests the participation of reactive oxygen species. Calcium-dependent signaling pathways such as those linked to calcineurin and PKC also contribute to NF-κB activation by depolarization, as assessed by blockade through pharmacological agents. These results suggest that NF-κB activation in skeletal muscle cells is linked to membrane depolarization and depends on the duration of elevated intracellular calcium. It can be regulated by sequential activation of calcium release mediated by the ryanodine and by IP3 receptors.

Ca(2+)- and pH-dependent halothane stimulation of Ca2+ release in sarcoplasmic reticulum from frog muscle

1996 ◽  
Vol 271 (2) ◽  
pp. C540-C546 ◽  
Author(s):  
M. Beltran ◽  
R. Bull ◽  
P. Donoso ◽  
C. Hidalgo
Keyword(s):  
Skeletal Muscle ◽  
Sarcoplasmic Reticulum ◽  
Calcium Release ◽  
Release Kinetics ◽  
Frog Muscle ◽  
Time Range ◽  
Frog Skeletal Muscle ◽  
Open Probability ◽  
Filtration System ◽  
Stimulation Of

The effect of halothane on calcium release kinetics was studied in triad-enriched sarcoplasmic reticulum vesicles from frog skeletal muscle. Release from vesicles passively equilibrated with 3 mM 45CaCl2 was measured in the millisecond time range by use of a fast-filtration system. Halothane (400 microM) increased release rate constants at pH 7.1 and 7.4 as a function of extravesicular pCa. In contrast, halothane at pH 6.8 produced the same stimulation of release from pCa 7.0 to 3.0; no release took place in these conditions in the absence of halothane. Halothane shifted the calcium activation curve at pH 7.1, but not at pH 7.4, to the left and increased channel open probability at pH 7.1 in the cis pCa range of 7.0 to 5.0. These results indicate that cytosolic pCa and pH modulate the stimulatory effects of halothane on calcium release. Furthermore, halothane stimulated release in frog skeletal muscle at low pH and resting calcium concentration, indicating that in frog muscle halothane can override the closing of the release channels produced by these conditions, as it does in malignant hyperthermia-susceptible porcine muscle.

Calcium-dependent halothane activation of sarcoplasmic reticulum calcium channels from frog skeletal muscle

1994 ◽  
Vol 266 (2) ◽  
pp. C391-C396 ◽  
Author(s):  
R. Bull ◽  
J. J. Marengo
Keyword(s):  
Skeletal Muscle ◽  
Sarcoplasmic Reticulum ◽  
Calcium Channels ◽  
Lipid Bilayers ◽  
Single Channel ◽  
Free Calcium ◽  
Frog Skeletal Muscle ◽  
Time Constants ◽  
Calcium Dependent ◽  
Open Time

The effect of halothane on calcium channels present in sarcoplasmic reticulum membranes isolated from frog skeletal muscle was studied at the single channel level after fusing the isolated vesicles into planar lipid bilayers. Addition of 91 microM halothane to the cytosolic compartment containing 1 microM free calcium activated the channel by increasing fractional open time from 0.11 to 0.59, without changing the channel conductance. The activation of the channels by halothane was calcium dependent. At resting calcium concentrations in the cytosolic compartment, halothane failed to activate the channel, whereas maximal activation was found at 10 microM calcium. The free energy of halothane binding to the channel decreased from -5.8 kcal/mol at 1 microM calcium to -6.6 kcal/mol at 10 microM calcium. Halothane increased the open time constants and decreased the closed time constants, indicating that it binds to both the open and the closed configurations of the channel.

Sarcoplasmic Reticulum Calcium Release Channels in Ventricles of Older Adult Hamsters

2006 ◽  
Vol 25 (1) ◽  
pp. 107-113 ◽  
Author(s):  
Peter A. Nicholl ◽  
Susan E. Howlett
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Older Adult ◽  
Binding Sites ◽  
Calcium Release ◽  
Ryanodine Receptors ◽  
Calcium Release Channels ◽  
Site Density ◽  
Age Related ◽  
Sarcoplasmic Reticulum Calcium ◽  
Age Related Changes

ABSTRACTWhether the density of sarcoplasmic reticulum (SR) calcium release channels / ryanodine receptors in the heart declines with age is not clear. We investigated age-related changes in the density of «3H»-ryanodine receptors in crude ventricular homogenates, which contained all ligand binding sites in heart and in isolated junctional SR membranes. Experiments utilized young (120 days) and older adult (300 days) hamsters. «3H»-ryanodine binding site density did not change with age in crude homogenate preparations, although total heart protein concentration increased significantly with age. In contrast, the density of «3H»-ryanodine binding sites decreased markedly in heavy SR membranes purified from older hearts. These results show that demonstration of age-related changes in cardiac ryanodine receptor density depends upon the preparation used. Furthermore, the increase in total ventricular protein with age suggests that normalization of data by membrane protein should be used with caution in studies of aging heart.

Superoxide-Induced Potentiation in the Hippocampus Requires Activation of Ryanodine Receptor Type 3 and ERK

2008 ◽  
Vol 99 (3) ◽  
pp. 1565-1571 ◽  
Author(s):  
A. Tara Huddleston ◽  
Wei Tang ◽  
Hiroshi Takeshima ◽  
Susan L. Hamilton ◽  
Eric Klann
Keyword(s):  
Calcium Channels ◽  
Calcium Release ◽  
Ryanodine Receptors ◽  
Hippocampal Slices ◽  
Long Term Potentiation ◽  
Calcium Flux ◽  
Functional Coupling ◽  
Area Ca1 ◽  
Term Potentiation ◽  
Subsequent Activation

Reactive oxygen species (ROS) are required for the induction of long-term potentiation (LTP) and behave as signaling molecules via redox modifications of target proteins. In particular, superoxide is necessary for induction of LTP, and application of superoxide to hippocampal slices is sufficient to induce LTP in area CA1. Although a rise in postsynaptic intracellular calcium is necessary for LTP induction, superoxide-induced potentiation does not require calcium flux through N-methyl-d-aspartate (NMDA) receptors. Ryanodine receptors (RyRs) mediate calcium-induced calcium release from intracellular stores and have been shown to modulate LTP. In this study, we investigated the highly redox-sensitive RyRs and L-type calcium channels as calcium sources that might mediate superoxide-induced potentiation. In agreement with previous studies of skeletal and cardiac muscle, we found that superoxide enhances activation of RyRs in the mouse hippocampus. We identified a functional coupling between L-type voltage-gated calcium channels and RyRs and identified RyR3, a subtype enriched in area CA1, as the specific isoform required for superoxide-induced potentiation. Superoxide also enhanced the phosphorylation of extracellular signal-regulated kinase (ERK) in area CA1, and ERK was necessary for superoxide-induced potentiation. Thus superoxide-induced potentiation requires the redox targeting of RyR3 and the subsequent activation of ERK.

scholarly journals Divalent cation activation and inhibition of single calcium release channels from sheep cardiac sarcoplasmic reticulum.

1990 ◽  
Vol 95 (5) ◽  
pp. 981-1005 ◽  
Author(s):  
R H Ashley ◽  
A J Williams
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Lipid Bilayers ◽  
Calcium Release ◽  
Single Channel ◽  
Fluctuation Analysis ◽  
Open Probability ◽  
Cardiac Sarcoplasmic Reticulum ◽  
Channel Opening ◽  
Lifetime Analysis ◽  
Single Channel Currents

Single Ca2+ release channels from vesicles of sheep cardiac junctional sarcoplasmic reticulum have been incorporated into uncharged planar lipid bilayers. Single-channel currents were recorded from Ca2(+)-activated channels that had a Ca2+ conductance of approximately 90 pS. Channel open probability increased sublinearly as the concentration of free Ca2+ was raised at the myoplasmic face, and without additional agonists the channels could not be fully activated even by 100 microM free Ca2+. Lifetime analysis revealed a minimum of two open and three closed states, and indicates that Ca2+ activated the channels by interacting with at least one of the closed states to increase the rate of channel opening. Correlations between adjacent lifetimes suggested there were at least two pathways between the open- and closed-state aggregates. An analysis of bursting behavior also revealed correlations between successive burst lengths and the number of openings per burst. The latter had two geometric components, providing additional evidence for at least two open states. One component appeared to comprise unit bursts, and the lifetime of most of these fell within the dominant shorter open-time distribution associated with over 90% of all openings. A cyclic gating scheme is proposed, with channel activation regulated by the binding of Ca2+ to a closed conformation of the channel protein. Mg2+ may inhibit activation by competing for this binding site, but lifetime and fluctuation analysis suggested that once activated the channels continue to gate normally.

scholarly journals RYR2 Proteins Contribute to the Formation of Ca2+ Sparks in Smooth Muscle

2004 ◽  
Vol 123 (4) ◽  
pp. 377-386 ◽  
Author(s):  
Guangju Ji ◽  
Morris E. Feldman ◽  
Kai Su Greene ◽  
Vincenzo Sorrentino ◽  
Hong-Bo Xin ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Calcium Release ◽  
Ryanodine Receptors ◽  
Wild Type ◽  
Calcium Dependent ◽  
Outward Currents ◽  
Associated Proteins ◽  
Kinetics Of ◽  
Spontaneous Transient Outward Currents

Calcium release through ryanodine receptors (RYR) activates calcium-dependent membrane conductances and plays an important role in excitation-contraction coupling in smooth muscle. The specific RYR isoforms associated with this release in smooth muscle, and the role of RYR-associated proteins such as FK506 binding proteins (FKBPs), has not been clearly established, however. FKBP12.6 proteins interact with RYR2 Ca2+ release channels and the absence of these proteins predictably alters the amplitude and kinetics of RYR2 unitary Ca2+ release events (Ca2+ sparks). To evaluate the role of specific RYR2 and FBKP12.6 proteins in Ca2+ release processes in smooth muscle, we compared spontaneous transient outward currents (STOCs), Ca2+ sparks, Ca2+-induced Ca2+ release, and Ca2+ waves in smooth muscle cells freshly isolated from wild-type, FKBP12.6−/−, and RYR3−/− mouse bladders. Consistent with a role of FKBP12.6 and RYR2 proteins in spontaneous Ca2+ sparks, we show that the frequency, amplitude, and kinetics of spontaneous, transient outward currents (STOCs) and spontaneous Ca2+ sparks are altered in FKBP12.6 deficient myocytes relative to wild-type and RYR3 null cells, which were not significantly different from each other. Ca2+ -induced Ca2+ release was similarly augmented in FKBP12.6−/−, but not in RYR3 null cells relative to wild-type. Finally, Ca2+ wave speed evoked by CICR was not different in RYR3 cells relative to control, indicating that these proteins are not necessary for normal Ca2+ wave propagation. The effect of FKBP12.6 deletion on the frequency, amplitude, and kinetics of spontaneous and evoked Ca2+ sparks in smooth muscle, and the finding of normal Ca2+ sparks and CICR in RYR3 null mice, indicate that Ca2+ release through RYR2 molecules contributes to the formation of spontaneous and evoked Ca2+ sparks, and associated STOCs, in smooth muscle.

Nitric oxide inhibits calcium release from sarcoplasmic reticulum of porcine tracheal smooth muscle cells

1997 ◽  
Vol 272 (1) ◽  
pp. L1-L7 ◽  
Author(s):  
M. S. Kannan ◽  
Y. S. Prakash ◽  
D. E. Johnson ◽  
G. C. Sieck
Keyword(s):  
Nitric Oxide ◽  
Smooth Muscle ◽  
Sarcoplasmic Reticulum ◽  
Calcium Release ◽  
Ryanodine Receptors ◽  
Tracheal Smooth Muscle ◽  
Nitric Oxide Donor ◽  
Ip3 Receptors ◽  
Video Fluorescence Microscopy ◽  
Inositol 1,4,5 Trisphosphate

In the present study, effects of the nitric oxide donor, S-nitroso-N-acetylpenicillamine (SNAP), on sarcoplasmic reticulum (SR) Ca2+ release were examined in freshly dissociated porcine tracheal smooth muscle (TSM) cells. Fura 2-loaded TSM cells were imaged using video fluorescence microscopy. SR Ca2+ release was induced by acetylcholine (ACh), which acts principally through inositol 1,4,5-trisphosphate (IP3) receptors, and by caffeine, which acts principally through ryanodine receptors (RyR). SNAP inhibited ACh-induced SR Ca2+ release at both 0 and 2.5 mM extracellular Ca2+. Degraded SNAP had no effect on ACh-induced SR Ca2+ release. SNAP also inhibited caffeine-induced SR Ca2+ release. ACh-induced Ca2+ influx was not affected by SNAP when SR reloading was blocked by thapsigargin. SNAP also did not affect SR Ca2+ reuptake. The membrane-permeant analogue of guanosine 3',5'-cyclic monophosphate (cGMP), 8-bromo-cGMP, mimicked the effects of SNAP. These results suggest that, in porcine TSM cells, SNAP reduces the intracellular Ca2+ response to ACh and caffeine by inhibiting SR Ca2+ release through both IP3 and RyR, but not by inhibiting influx or repletion of the SR Ca2+ stores. These effects are likely mediated via cGMP-dependent mechanisms.

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